X-ray photography in which an object is irradiated with X-rays and an intensity distribution of X-rays transmitted through the object is detected to obtain an X-ray image of the object has been widely used in the medical field and the industrial field. Methods for obtaining an X-ray image started with the film-screen method in which a light-sensitive film on which visible light emitted from a rare-earth phosphor sensitive to X-rays is incident undergoes chemical development to form a visible image. Since then, new methods have been developed through technological innovation. Among them, imaging apparatuses using a flat panel detector (FPD), which are based on semiconductor process technology, are available. The FPD is configured such that pixels each having a small photoelectric conversion element and a switching element are arranged in a grid pattern. Because of the significantly wider dynamic range than that of imaging apparatuses based on light-sensitive films of the related art, such imaging apparatuses have an advantage of the formation of stable X-ray images even if the amount of X-ray exposure changes. In addition, because of no need for chemical treatments, the imaging apparatuses also have an advantage of the immediate formation of X-ray images.
X-ray imaging apparatuses can be classified into the following types: a stationary type that is installed in a desired place such as in a standard radiography room, and a transportable type that can be freely moved. In recent years, the demand for transportable X-ray imaging apparatuses (hereinafter referred to as “electronic cassettes”, or “cassettes” for short) has increased.
In the related art, an electronic cassette is electrically connected to a control unit via a cable used for feeding electric power from an external source and establishing communication with the control unit. Complicated cable wiring may cause a problem when an electronic cassette is used from place to place, and too long a cable may cause a situation where users may accidentally trip on the cable, leading to a possibility of the cable, the cassette, or the control unit being damaged.
In a clean (sterilized) environment such as in an operating room, furthermore, it is not desirable that a radiographic system including cables be in contact with an open (unsterilized) area such as the floor.
Recently, wireless cassettes configured to use a built-in power supply unit, instead of a cable, and adapted for wireless communication have emerged and are expected to markedly increase the flexibility of X-ray imaging. However, the stability of wireless communication is less than that of wired or cable connections which ensure physical connections, and the remaining battery level of the built-in power supply unit changes with time. Measures against these difficulties need to be taken.
The above problems have been addressed by Japanese Patent Laid-Open No. 2005-208269, Japanese Patent Laid-Open No. 2006-263322, and Japanese Patent Laid-Open No. 2009-201968, which disclose a drive control method to address an insufficient remaining battery level of a built-in power supply unit and a technology for displaying a state on an external control device.
However, in order to improve the imaging efficiency, it is important to quickly check the conditions of a cassette on the main body of the cassette. In an environment where a plurality of wireless cassettes are used under a single control device, it is desirable to immediately check which cassette the control device is communicating with or whether or not the X-ray sensor of the cassette that the control device is communicating with is correctly operating.
It is also desirable to take measures against less stability of wireless communication than that of wired connections which ensure physical connections and against the changes in the remaining battery level of the built-in power supply unit over time.